How long does first cl mail take to arrive?

Okay I am not from England but if it works on the same premise as the U.S. postal service & you ordered on Sun. they would not go into mail until Mon. shipped from there to your locale & reach there on Tues. Sorted & sent for delivery on Wed. so you should have them by Wed. post or Thur. at the latest if this is a legitimate Ticket seller. So you should have them on time for Sun*